This invention is related generally to a novel process for the production of aliphatic polyamines from an aliphatic amine reactant+a nitroalkane+an aldehyde. The term "polyamine" is used to connote a compound with at least one terminal primary amine group and one or more secondary amine groups irrespective of the intermediate alkylene, cycloalkylene, alkyleneimine, or cycloalkyleneimine structure of the compound. Prior art processes have used analogous reactants for the production of aliphatic polyamines by first making an alkanolamine intermediate. Our novel process does not do so. We make a salt intermediate, details of which, and the process are set forth hereinbelow.
Though a primary or secondary amine is an acceptable starting material in both processes, reliance on formation of an alkanolamine intermediate in the prior art process results in a slow reaction and poor yields of nitroamine. Our process relies on the pre-formation of the salt intermediate by protonation of the amine starting material by the nitroalkane, and addition of aldehyde to the salt intermediate has been found to be a more direct route to the corresponding nitroamine, which route is unexpectedly more efficient than the prior art process starting with analogous reactants.
Specifically, this invention relates to the conversion of only aliphatic amine reactants to nitroamines, which are subsequently hydrogenated to aliphatic polyamines. The invention is unrelated to the conversion of arylamines to arylimines which can form nitroamines which in turn may be hydrogenated. Arylimines are stable, particularly under basic conditions, while polyamines are readily polymerized under such conditions, thus are recognized to be distinct from arylimines.
More specificially, this invention relates to the production of polyalkylene polyamines ("PAPA"), particularly those synthesized from other PAPA, and still more specifically to a unique mixture of an acyclic (or noncyclic) mononitroamine and a dinitroamine (referred to herein as "nitroamine mixture" or "first mixture"). From this first mixture is derived a second mixture of (A) a dialkylenetriamine having one disubstituted terminal carbon atom adjacent a primary amine group at one end, and (B) a trialkylenetetramine having two disubstituted terminal C atoms each adjacent a primary amine group at each end (referred to herein as "PAPA mixture"). The term "polyalkylenepolyamine (PAPA)" is specifically used to connote a polyamine with at least three amine groups interconnected with acyclic or cyclic alkylene groups.
A variation of the Mannich reaction has been used in the prior art to produce nitroamines which could then be hydrogenated to produce PAPA. The Mannich reaction involves condensation of a carbonyl compound, for example acetophenone, with formaldehyde and ammonia or a primary or secondary amine. The reaction was modified to improve its selectivity. In the formation of a nitroamine, aqueous formaldehyde is slowly added to an amine (for example, isopropylamine), thus forming the aminoalkanol. 2-nitropropane is then added to the flask at one time and the reaction mixture worked up to yield N-(2-nitroisobutyl)isopropylamine. But successful results have been limited to the use of monoamines which yield mononitro compounds, and then, upon hydrogenation, to diamines. It is evident that the reaction with alkylamines is slow, since the general procedure requires the reaction mixture to stand for several days, and the slow reaction is prone to allow the polymerization of alkylimines formed; where an aryl diamine is used, a more stable arylimine is formed which permits heating the reaction mixture and improving rates. See "Reaction of Primary Aliphatic Amines with Formaldehyde and Nitroparaffins" by Murray Senkus; "id. II. Secondary Amines" by Hal G. Johnson; and, "The Preparation and Reduction of Nitro Amines Obtained from Aromatic Amines, Formaldehyde, and Nitroparaffins" by Hal G. Johnson; J.A.C.S., Vol. 68, 10-17 (Jan 1946).
The order of addition of the reactants, namely aldehyde to amine, and finally the nitroalkane, derived from the work of Henry, Ber., 38, 2027 (1905) which required the formation of the alkanolamine first. Several workers identified in the Senkus article, supra, in later years continued experimentation with the basic reaction but always first added the aldehyde to the amine, and then the nitroalkane when preparing aliphatic polyamines. Because of their predisposition relative to the pre-preparation of the alkanolamine as the intermediate in the preparation of aliphatic polyamines, they were unaware that a change in the order of addition, which change resulted in bypassing the formation of the alkanolamine, would be responsible for a faster reaction and better yields of the desired nitroamine product. Moreover, this change in the order of addition provides better results whether the amine is primary or secondary, alkyl or aralkyl, or an acyclic or cyclic aliphatic amine.
The order of addition was changed by Johnson, supra, in the preparation of N-(2-nitroisobutyl)-aniline from aniline, formalin, and 2-nitropropane, when -he heated one mol aniline, and one mol 2-nitropropane 300 ml methanol as solvent, in the presence of trimethylbenzylammonium hydroxide (TMBAH), then added the formalin. He thus formed the arylimine the stability of which was maintained under basic conditions by addition of the TMBAH, until the arylimine is attacked by the nitropropane to form the nitroamine. Under basic conditions, aliphatic polyamines are polymerized. Thus, the mechanism for the reaction, is quite different from that for an aliphatic amine, and is dictated by the order of addition.
PAPA are commercially produced by the reaction of ethyleneimine and ammonia, a large excess giving mainly ethylenediamine (EDA), and progressively smaller ratios of ammonia to ethyleneimine resulting in the higher homologs, such as diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), and pentaethylenehexamine (PEHA); hexaethylenepentamine (HEPA), or, PAPA are formed as by-products of the reaction of 1,2-dichloropropane (ethylene dichloride) with ammonia (in excess) which yields EDA; or, as byproducts of the reaction af an alkanolamine and ammonia in the presence of hydrogen and a catalyst, as for example described in U.S. Pat. No. 4,014,933. Also produced, along with the acyclic PAPA (such as DETA, linear and branched TETA and higher homologs), are piperazine, aminoethylpiperazine, and cyclic polyethylene polyamines which are not particularly desirable even if they were easy to separate--and they are not.
PAPA, and polyethylene polyamines in particular, are now widely used as emulsifiers, vulcanization accelerators, curing agents for epoxy resins, fungicides, etc. The demand for PAPA has spurred the development of numerous processes for making them, usually by the catalyzed reaction of an alkanolamine, ammonia and an alkyleneamine, disclosed for example in U.S. Pat. Nos. 3,714,259; 3,766,184; 4,036,881; 4,044,053; 4,314,083; and 4,324,917; inter alia, none of which is particularly well-suited for the production of a diprimary triamine with a disubstituted N-adjacent terminal carbon atom, or, a diprimary tetramine with disubstituted terminal N-adjacent carbon atoms. Nor is a process of any of the aforesaid patents stated to be suitable for production of such PAPA. Moreover, each of the patents requires that at least the C atom adjacent the primary amino group of the alkyleneamine have at most only one substituent; and, that the terminal C atom adjacent the terminal N atom of the alkanolamine, likewise have at most only three substituents including the amino group. Evidently, the catalytic reaction does not proceed satisfactorily if the N-adjacent terminal C atom was disubstituted.
One would think that simply substituting a diprimary amine, say EDA, for the isopropylamine used in the modified Mannich reaction referred to hereinabove, would provide a triamine with at least one terminal disubstituted terminal N-adjacent C atom. And it does. Except that it also produces many undesirable byproducts. A diamine such as 1,3-diaminopropane (1,3-PDA) or 1,2-propane diamine (1,2PDA) produces many more cyclic byproducts than does 1,2-ethanediamine.
Similarly, one would expect that substituting a triamine, for example DETA (diethylene triamine), would provide a tetramine with each N-adjacent terminal C atom being disubstituted. And it does. Except that the amount of compound with disubstituted N-adjacent terminal C atoms is formed in so small an amount relative to the unwanted byproducts that separation is not practical, and if recovered would be uneconomical.
Specifically, to make a mixture of particular PAPA through an alkanolamine intermediate, seemed to fly in the face of Cerf de Mauny's rule which states that the number of hydroxymethylamine groups that would react with a nitroalkane is one less than the number of hydrogen atoms linked to the carbon atom to which the nitro group is attached. Because we subscribed to the theory that it was necessary first to form the alaknolamine intermediate, we added aqueous formaldehyde to the organic amine reactant, and the nitroalkane last. Our efforts still met with poor conversions and very slow reaction times until we realized that the key to obtaining better conversion to the nitroamine was adding the aldehyde last, and gradually. It is more preferable to use an essentially solvent-free monoaldehyde, that is an aldehyde with a single --CHO group, and preferably an aldehyde in solid form, such as paraformaldehyde which has a single --CHO group in the repeating unit. By "solvent-free aldehyde" we refer to an aldehyde which is substantially insoluble (less than 5% by weight) in the liquid, typically a lower alkanol, in which the amine and nitroalkane form a salt. When only the organic amine reactant and nitroalkane are present as a mixture along with the salt formed, the amine and nitroalkane liquid is "the liquid" in which the aldehyde is insoluble though it reacts with the salt.
The commercial importance of making the acyclic PAPA which one needs, and at the same time not making a substantial amount of byproducts, cannot be overemphasized. It is therefore serendipitous that a mixture of two highly desirable PAPA can be made with a single, particular diprimary diamine, namely EDA which is premixed with a nitroparaffin to form a salt, which in turn reacts with a solid aldehdye, added gradually under specified conditions; and, that the salt has the unique property of forming the desired mixture with more than 90 mol % yield, and preferably with a yield of less than 5 mol % to unwanted nitroamine byproducts.